This invention relates to moisture vapor permeable dressings used in surgical and general medical applications such as bandaging and the like.
It is well recognized in the field of bandaging, wound healing, surgical incise drapes and similar sheet materials that in promoting healing processes the wound dressing or bandage should have characteristics closely resembling skin. One such characteristic is moisture vapor permeability which defines a condition wherein the dressing or the like will transmit water vapor therethrough so that maceration of the wound does not occur. On the other hand, the dressing should be sufficiently continuous in order to prevent the entrance of bacteria into the wound which may cause infection.
Moisture vapor permeability can be provided to wound dressings, surgical drapes and the like by two separate routes. One such route is by providing a microporous structure as the bandaging material or wound dressing, which pores allow moisture vapor to pass therethrough from the wound and into the atmosphere. The degree of microporosity, particularly the size of the pores, is particularly important since if the pores are too large, liquid water and bacteria may penetrate through the structure into the wound, thus increasing the risk of infection. When the micropores are sufficiently small, the desirable result is that moisture vapor will pass through the micropores from the wound, but bacteria and liquid water cannot pass through the micropores from the dressing surface into the wound.
Another means of providing moisture vapor permeability to a dressing is by having the dressing constructed of a material which is continuous, i.e. nonmicroporous which passes water vapor at a molecular level from molecular chain to molecular chain. This type of moisture vapor permeability is the desired type of moisture vapor permeability since it eliminates regulation of pore size to prevent entrance of bacteria and liquid water into the wound. Such moisture vapor permeability without micropores is alluded to in U.S. Pat. No. 3,645,835. However, one of the drawbacks of continuous moisture vapor permeable dressings is that although they have moisture vapor permeability, they do not have sufficient moisture vapor permeability, i.e., approaching that of human skin, to be completely effective in preventing maceration of the wound.
True moisture vapor permeability is provided by a dressing which acts as a membrane through which moisture will pass at a specific rate and, therefore, the moisture vapor transmission rate of the dressing is not contingent upon the thickness of the dressing.
Although moisture vapor permeable dressings have been made which are microporous such as disclosed in U.S. Pat. No. 3,121,021 with high moisture vapor permeability, there has been great difficulty in providing a dressing with high moisture vapor permeability i.e. over 300 and preferably over 500 g/m.sup.2 /24 hours at 40.degree. C. which is nonmicroporous, i.e. continuous.
In addition, in the most desired instance the dressing is composed of some type of polymeric sheet material with an adhesive on one side by which the dressing will adhere to the skin. Thus, if a dressing is to be continuous rather than microporous in all instances, the sheet material and the adhesive must be moisture vapor permeable at the molecular level.
In accordance with the present invention, a moisture vapor permeable sheet material which is continuous and can be made optionally microporous, is provided which has moisture vapor permeability in its truest sense and which can also include an adhesive which is also continuous and moisture vapor permeable.
In addition to being moisture vapor permeable, one of the constituents of the dressing also provides desirable effects upon wound healing.